PureBasic

Large Persistent Hash Table Stored on Filesystem

See more Misc Examples

Demonstrates how to implement a large, persistent hash table that is stored on the filesystem and allows for quick retrieval using a hash key. PureBasic

IncludeFile "CkCache.pb"

Procedure ChilkatExample()

    success.i = 0

    ; Let's say we would like to implement a persistent hash table with approximately 200,000 entries.
    ; We want something simple and straightforward.
    ; 
    ; The Chilkat Cache class is a solution that might fit.
    ; 
    ; Each hash table entry is a file.  Depending on the number of anticipated hash entries,
    ; the files can be contained in a single directory, or a collection of 256 directories,
    ; or a collection of 256x256 directories.

    ; There are 3 options:
    ; 
    ; Level 0: All cache files are in a single directory (the cache root).
    ; Level 1: Cache files are located in 256 sub-directories numbered 0 .. 255 directly under the cache root.
    ; Level 2: There are two levels of sub-directories under the cache root. 
    ;          The 1st level has 256 sub-directories numbered 0 .. 255 directly under the cache root. 
    ;          The 2nd level allows for up to 256 sub-directories (0..255) under each level-1 directory. 
    ;          Cache files are stored in the leaf directories. 

    ; For this example, given that we anticipate a larger number of hash entries, we choose a "level 2" cache.
    cache.i = CkCache::ckCreate()
    If cache.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; We can also spread the cache among several root directories, but for this example we'll only use one root directory.
    ; Call AddRoot once for each root directory.
    CkCache::ckAddRoot(cache,"c:/temp/myCache")
    CkCache::setCkLevel(cache, 2)

    ; Add some key/values to the persisted hash table (i.e. the cache).
    ; The eTag is optional metadata.
    key.s = "apple"
    eTag.s = ""
    itemValue.s = "macos"
    success = CkCache::ckSaveTextNoExpire(cache,key,eTag,itemValue)

    ; Add more items..
    success = CkCache::ckSaveTextNoExpire(cache,"microsoft","","windows")
    success = CkCache::ckSaveTextNoExpire(cache,"google","","android")

    ; Lookup items:
    key = "microsoft"
    itemValue = CkCache::ckFetchText(cache,key)
    Debug key + ": " + itemValue

    key = "apple"
    itemValue = CkCache::ckFetchText(cache,key)
    Debug key + ": " + itemValue


    CkCache::ckDispose(cache)


    ProcedureReturn
EndProcedure